NASA Lewis Research Center's On-Board Propulsion program (OBP)
is developing low-thrust chemical propulsion technologies for
both satellite and vehicle reaction control applications. There
is a vigorous international competition to develop new, high-performance
bipropellant engines. High-leverage bipropellant systems are critical
to both commercial competitiveness in the international communications
market and to cost-effective mission design in government sectors.
To significantly improve bipropellant engine performance, we must
increase the thermal margin of the chamber materials. Iridium-coated
rhenium (Ir/Re) engines, developed and demonstrated under OBP
programs, can operate at temperatures well above the constraints
of state-of-practice systems, providing a sufficient margin to
maximize performance with the hypergolic propellants used in most
satellite propulsion systems.
For the near term, the OBP program is focused on transferring
Ir/Re technology to the user community. This effort includes the
development of low-cost fabrication and joining technologies,
the generation of Re mechanical properties, and critical technology
demonstrations. Lightweight, low-volume, high-pressure bipropellant
engine technology is also being developed for small-satellite
applications requiring high thrust. This effort targets 200- to
500-kg satellites to be launched on inexpensive, volume-limited
launch vehicles.
For the long term, the OBP program is developing chamber materials
for long-life operation in combustion environments that are more
energetic and oxidizing than hypergolic propellants. The long-range
goal is to develop a material system that can run any propellant
combination at any mixture ratio.
In addition to the bipropellant efforts, OBP is also developing
high-performance, nontoxic, monopropellant systems to replace
state-of-practice hydrazine (N2H4)
monopropellant thrusters. The monopropellants under consideration
are based on liquid gun-propellant formulations, which are environmentally
friendly, have a high density, and have better thermal characteristics
than hydrazine. The near-term goal is to transfer a "green"
system to improve mission performance and greatly reduce ground
operations costs. For the far-term, a very high performance (high
specific impulse) system is being sought. The key to this goal
is the development of a high-temperature catalyst; research in
this area is underway.
For very small spacecraft and microspacecraft, several chemical propulsion technologies that provide performance and system benefits are being explored. Examples include (1) a warm gas propulsion system that uses a mixture of hydrogen, oxygen, and an inert gas (nitrogen or helium) and that offers a high specific impulse alternative to state-of-practice cold gas systems with a minimal increase in complexity; (2) exothermic decomposing solid and hybrid systems, which offer the high density and simplicity of solid propellants for low-thrust, quick-response applications; (3) a water electrolysis concept that can provide dual use as a combined propulsion/power system; and (4) a microturbomachinery-based bipropellant system for very high-performance applications which uses microelectronic mechanical system (MEMS) fabrication technology to provide propulsion systems "on-a-chip" similar to computer chips.
Previous articleLast updated April 30, 1997
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